Lung pathology is a significant cause of the morbidity and mortality associated with acute respiratory virus infection. Respiratory viruses, such as influenza virus not only cause damage to the epithelium, but activate immune defense mechanisms. Although these immune mechanisms are employed to destroy and remove infected cells in an attempt to clear the virus, they can also promote lung pathology. However, the key cellular and molecular mechanisms that regulate the balance between protection and tissue damage during acute viral infection remain poorly understood. This lack of knowledge severely limits the development of novel therapies to treat the disease. Therefore, understanding the fundamental mechanisms whereby respiratory viral infection induces lung damage is critical for the development of improved therapies for treatment of disease. Our exciting and intriguing preliminary results suggest that the lymphotoxin beta receptor, LTR, a member of the TNFR superfamily, promotes influenza-associated lung damage. The overall objective of this proposal is to define how LT?R controls lung damage associated with influenza infection. Our working hypothesis is that LT?R signaling in respiratory epithelial cells inhibits mucus production during influenza infection allowing for elevated viral replication and increased lung damage. To test this hypothesis, we propose two specific aims. In Aim 1, we will use biochemical and genetic approaches to determine the impact of LT?R signaling on mucus production and viral replication. In Aim 2, we will test that LT?R signaling in respiratory epitheial cells is essential to promote lung immunopathology during influenza infection. We propose that LT?R signaling in respiratory epithelial cells promotes viral replication and induction of potent inflammatory responses which cause severe lung damage. Completion of these aims will define the LT?R-dependent mechanisms that contribute to lung damage. The research proposed is significant, because it will provide a deeper understanding of the mechanisms regulating virus-induced immunopathology and will help in developing new immunotherapeutic strategies to control respiratory disease.